The food conservation industry includes the production of worked or semiworked food pieces, consisting in pieces of food of desired dimensions, generally called chunks. This production is very commonly used in all fruit processing as well as tomatoes.
After cubing the food proceeds to sterilization and thereafter to storage, undergoing the latter two processes mixed with a liquid, consisting of the juice of the product itself produced during cubing, together with other sterile liquids.
This liquid mixture enables transport of the chunks to be effected without having to resort to using high-pressures which might damage them, and furthermore guarantees sterility during transport along a sterilization plant where the product is subjected to heating and cooling phases before being stored in bags or barrels by means of filling machines, also operating under conditions of absolute sterility.
Before the filling operation can begin, however, the chunks have to be separated from the liquid mixture, and this is performed using drainage devices essentially comprising two concentric cylinders.
The internal cylinder is generally provided with spaced bars forming a grill. The chunks and liquid are introduced therein and the liquid drains down into the external cylinder, whereupon it is removed by an extraction pump, while the chunks are removed from the internal cylinder by a pump which also regulates the outflow rate thereof.
With known-type drainage devices it is difficult to obtain a regular drainage rate which keeps a very low and constant quantity of residual liquid while maintaining a constant outflow rate of the drained chunks.
Constant drainage regulation depends principally on the difference in pressure existing in the outflow conduit for the chunks and in the liquid collection cylinder. This pressure difference can vary for various reasons, such as a partially blocked grill, or to an increase or decrease in the chunk-liquid ratio.
Up to now, in order to keep the pressure as constant as possible, it has only been possible to act directly on the two pumps, which creates obvious difficulties in regulation as well as unpredictable response to such regulation.